I've made a crucial mistake in that I'm brewing a batch while I have another in a secondary.

Issue: I forgot to puchase an additional airlock when I was at the brew store over the weekend. Any short term fixes for the now? If I remove airlock from secondary, what is best way to keep it from getting infected until I can buy another air lock tomorrow.

regarding removing the airlock from the secondary, just leave it there. In a pinch, loosely cover your primary fermenter opening with sanitized foil and replace it with the airlock you'll be buying tomorrow.

[QUOTE=jbaysurfer;4330800]regarding removing the airlock from the secondar

This is the best idea, the fermentation will produce gasses that will prevent anything bad from getting in while you get your airlock. Better yet, as mentioned look up blow off tube and get in the habit of using one of those for your primary, no more exploding airlocks